1. Field of the Invention
This invention is directed to the structure, known in the art as the cartridge assembly, for reciprocating the plunger used in forming parisons during the manufacture of glass containers with individual section (I.S.) machines.
2. Description of Related Art
A well-established process for manufacturing glass containers is known as the “blow-and-blow” process. In the “blow-and-blow” process, a gob of molten glass is introduced and partially shaped or molded into an object called a parison, which eventually will be formed into a glass container. The parison is formed by a blowing operation in a mold. The gob is introduced into the mold positioned over a plunger and neck ring which act together to form the neck region of the parison. Air pressure over the gob or a vacuum below the gob is provided to urge the gob into the neck and around the plunger. The plunger is then withdrawn creating a space into which air is blown to expand the gob to the shape of the mold cavity. Thereafter, the shaped gob or parison is transferred to a finishing mold for a further blowing operation to form the parison into a container.
The cartridge assembly must move the plunger and the thimble that slides over the plunger through three distinct positions; namely, “full-up”, “blow”, and “full-down” or retracted. In the full-up position, the thimble abuts the neck ring and the plunger is placed within the neck ring. In the blow position, the thimble remains abutting the neck ring but the plunger is partially withdrawn. In the full-down position, the thimble and plunger are moved clear of the neck ring so that the parison can be moved by an inverted arm to a container-forming station.
Various prior art cartridge assemblies for plunger and thimble cycling are disclosed, for example, in Colchagoff U.S. Pat. No. 3,305,344 entitled “Neck Mold and Plunger Unit for Glass Forming Apparatus”, Kozora U.S. Pat. No. 5,358,543 entitled “Air Tube Structure in a Glass Container Forming Machine” and Bolin U.S. Pat. No. 5,411,564 entitled “Pneumatic Plunger Mechanism for a Glassware Forming Machine.”
The Colchagoff patent discloses a cartridge assembly that moves the plunger and thimble with two separate single-acting, spring-biased pneumatic cylinders. The Kozora patent discloses a cartridge assembly with a single pneumatic piston and large and small springs for separately biasing the thimble and plunger in a well-known lost motion arrangement. When the plunger and neck ring are in the full-up position, the large spring is partially expanded and the small spring is compressed. Both springs hold the plunger and thimble in their upwardmost positions. As the plunger is drawn down to the blow position, the large spring is compressed but the small spring expands to maintain the thimble against the neck ring. As the piston is drawn down further, the thimble is captured and pulled down along with the plunger.
The main problem with single acting pneumatic pistons and return springs in cartridge assemblies is that there exists the tendency for a repeated hammering effect between the mechanical components which can and do lead to failure of various mechanical components. In particular, the floating piston actuated by the large spring bangs against the cylinder cap each time the plunger and neck ring are raised to the full-up position. Further, the repeated movement of the springs and the associated machine elements results in fatigue and wear of those components, especially if they tend to wobble during reciprocation.
The Bolis patent is directed to overcoming the hammering effect by elimination of springs altogether. The Bolis patent discloses a cartridge assembly that moves the plunger and thimble with two double acting pneumatic cylinders. However, the backward compatibility of the Bolis patent is limited by the need for controlling the pneumatic pressure in three, not just one, pneumatic pistons. Moreover, numerous parts exterior to the cartridge assembly would have to be replaced in the existing fleet of I.S. machines.